X-ray system for reducing steepness of wave front



Feb. 4, 1936.

M. MORRISON X RAY SYSTEM FOR REDUCING STEEPNESS OF WAVE FRONT FiledMarch 25, 1932 Source INVENTOR MV/VTFO/Vfl M0 3/5 0/ ATTORNEY PatentedFeb. 4, 1936 X-RAY SYSTEM FOR REDUCING STEEP- NESS OF WAVE FRONT rationof Delaware Application March 25, 1932, Serial No. 601,071

14 Claims.

This invention relates to X-ray apparatus and particularly to an X-raysystem for taking short exposure radiographic pictures.

In systems of this general type high potential heavy current electricalenergy is usually employed to energize the X-ray tube for a brief periodof time. The apparatus usually employed is a suitable switching means inthe high tension circuit to suddenly connect the Y-ray tube to thesource of electrical energy and enable the current supplied by thelatter to flow between the electrodes of the X-ray tube.

Heretofore in such systems upon closure of the switching means thesudden flow or surge of the high potential heavy currents occasionallycauses deleterious results to the tube. This is due primarily to theliberation of gases within the tube itself upon energization by theseheavy currents resulting in puncture of the envelope and destruction ofthe tube. Frequently the emission of electrons from the cathode due tothe surge of heavy current is so great that the cathode itself becomesdisrupted.

The sudden rush of current through the X-ray tube upon closure of theswitching means is initially so great that the rise of the energy fromzero to maximum is so rapid as to be analogous to a portion of the waveform having a frequency of the order of millions of cycles per second.

I have found that if the steepness of this wave front, as it is commonlyreferred to in the art, is materially lessened for a brief period oftime regardless of the minuteness thereof and the energy supplied to thetube is permitted to gradually rise the possibilities of destruction ofthe X-ray tube are obviated.

It is accordingly an object of my invention to provide an X-ray systemin which the X-ray tube is suddenly energized by high potential heavycurrent energy and in which the energy supplied to the latter ispermitted to gradually rise in a minute period of time.

Another object of my invention is to provide means associated with theX-ray tube adapted to reduce the steepness of the wave front of theenergy supplied to the X-ray tube.

Another object of my invention is to provide an X-ray system for takingshort exposure X-ray photographs in which the initial flow of thecurrent from a suitable source is short circuited around the X-ray tubefor a minute period of time.

Another object of my invention is to provide an X-ray system for takingshort exposure X-ray photographs in which the initial flow of thecurrent from a suitable source is short circuited around the X-ray tubefor a minute period of time and the energy supplied to the X-ray tube ispermitted to gradually rise in an equally short period of time afterexpiration of the period of short circuiting of the tube.

A further object of my invention is to provide an X-ray system in whicha steep wave front of the energy supplied to the X-ray tube is preventedupon connection of the latter to a source of high potential heavycurrent energy and to shield the cathode from these heavy currentsduring the initial surge thereof to prevent deleterious results to theX-ray tube.

Still further objects of my invention will become apparent to thoseskilled in the art by reference to the accompanying drawing wherein thesingle figure is a diagrammatic representation of an X-ray systemutilizing an embodiment of my invention.

Referring now to the drawing in detail I have shown a suitable source ofelectrical energy for supplying high potential heavy current electricalenergy, such as a high tension transformer 5, the primary winding 6 ofwhich is connected to a suitable source of alternating current ofcommercial potential by means of a pair of conductors LI and L2. Thesecondary winding 1 of this high tension transformer is arranged tostore uni-directional energy in a pair of condensers 8 and 9 ofrelatively large capacity during one half wave of the alternatingcurrent cycle.

One end of the secondary winding 1 is con nected, by means of aconductor IE, to the condenser 8 through a suitable rectifying valve [2and the opposite end of the secondary winding is similarly connected bymeans of a conductor l3 to the condenser 9 through a rectifying valve M.The condensers 8 and 9 are connected by means of a conductor I5 to themid-point of the secondary winding 1. The thermionic cathodes of therespective rectifying valves l2 and I4 receive heating currents from asuitable source of low tension energy, such for example as batteries orlow tension transformers IS, the primary windings of which may beconnected to the source of supply LI and L2, if desired.

During alternate half waves of the alternating current cycle thesecondary winding 1 will store energy in the condensers 8 and 9respectively, as is well known in the art. Suitable switching means,such as a mechanically operated switch, shown generally at I1 isarranged to connect this source of high potential heavy currentelectrical energy to an X-ray tube, such as shown at l8.

Although any suitable switching means, such as a vacuum switch, may beemployed with equal facility I have shown a mechanically operated switchwhich comp-rises a shaft E9, of suitable insulating material journalledin a pair of bearings 29, which in turn are supported by brackets 22 andthe shaft is is rotatably operable by means of an insulated handle 23.

A pair of spherical contact terminals 2 and 25 are rigidly secured tothe insulated shaft i9 and are rotatable therewith. These contactterminals are connected by means of conductors 23 and 2? to the sourceof high potential heavy current energy comprising the condensers 8 and 9respectively. A pair of stationary spherical contact terminals 28 and 29are positioned in such a manner as to be contacted by the terminals 24and 25 carried by the insulated shaft l9 upon rotation of the latter.

The contact terminal 28 is connected by means of a conductor 39 to thecathode electrode of the X-ray tube It and the contact terminal 29 isconnected by means of a conductor 32 to the anode electrode of the X-raytube 58. A resistance element 33 is connected in series with the contactterminal 29 and the anode of the X-ray tube for a purpose to behereinafter more fully set forth.

The cathode of the X-ray tube i8 is arranged to receive heating currentfrom a suitable source,

such as a battery or'a low tension transformer 34, the primary of whichmay be connected to the source of supply, such as the conductors Li andL2 in the same manner as the source of cathode heating energy IB for thevalve rectifiers l2 and M.

A capacitance element, such as a condenser 35, is connected between theconductors 33 and 32 and is thus in electrical shunt or parallelrelation with respect to the X-ray tube i8 and the source of energytherefor. A condenser 36 of somewhat larger capacity than the condenser35 is also connected in a shunt circuit relative to the cathode of theX-ray tube l8 and the source of heating energy therefor. The operationof the system just described for the taking of radiographic pictures isas follows:

Assuming that the switching device H is in the open position as shown inthe drawing, a suitable switch, not shown, in series with the primarywinding 6 of the high tension transformer 5 is first closed allowingenergy to be supplied through the conductors LI and L2 to the primarywinding 5. This in turn energizes the secondary winding 1 and duringalternate half waves of the alternating current cycle energy will besupplied to the secondary winding through the respective rectifyingvalves l2 and it to the condensers 8 and 9, respectively. Thesecondensers being of relatively large capacity of the order of amicrofarad at a potential of between 75 and 160 kilovolts becomecompletely charged with this voltage. When it is desired to energize theX-ray tube the insulated shaft i9 is rotated by means of the handle 23.This rotation establishes contact between the respective sphericalcontact members 24 and 28, and 25 and 29, respectively.

The high potential electrical energy stored in the condensers 8 and 9thus suddenly discharges through the X-ray tube l8. This circuit may betraced from the condenser it through conductor ,26, contact terminals 24and 23, and conductor 30 to the X-ray tube is, thence back to condenser9 through conductor 32, resistance element 33, contact terminals 29 and25, and conductor 27. This sudden surge of the high potential energy,

upon the sudden closing of the switch, would under usual conditionscause a sudden rise of the current from zero to maximum on flowingthrough the X-ray tube with a resulting wave front analogous to aportion of the wave form of millions of cycles per second which maydisrupt the tube.

The purpose, therefore, of the condenser 35 Which is connected in ashunt circuit with the X-ray tube and the high tension source is toprevent the steepness of this wave front. As the resistance of thecondenser 35 is much less than that of the X-ray tube to the initialsurge of energy, the closure of the switch ll, will cause this condenserto first take a charge, and as the latter tends to reach its maximumcapacity the current then flows through the X-ray tube. This condenser35 is of such capacity that current flows through the X-ray tube beforethe same reaches its maximum and after the condenser becomes completelycharged the entire energy is supplied to the X-ray tube. After therespective condensers 8 and 9 have completely discharged their entireenergy the condenser 35 likewise discharges through the X-ray tube.

It can thus be appreciated that upon the initial surge of the energyfrom the condensers a and 9, upon closure of the switch, the condenser35 acts for a minute period of time as a short circuit for the X-raytube.

through the X-ray tube, gradually rising from zero to maximum in anequally minute period of time.

The function of the condenser 35 although operable for a very briefperiod of time thus reduces the steepness of the wave front of theenergy supplied to the tube and the same, although in itself of briefduration, nevertheless gradually rises and obviates the possibilities ofdeleterious results to the X-ray tube due to the steep wave front of theinitial surge.

The condenser device 36 which is connected in shunt circuit with thecathode also receives a portion of the initial energy supplied to theX-ray tube and helps to prevent high voltage from being built up acrossthe filamentary cathode, which would otherwise occur due to theemployment of the steep wave front of the energy supplied to the tube asheretofore mentioned. This, therefore, prevents the high potentialdischarge current, when supplied to the X-ray tube, from injuring thecathode.

The resistance element 33 functions in the high tension circuit as ameans for preventing oscillations in the high tension circuit fromaffecting the supply of energy from the high tension source. Althoughthis resistance element 33 prevents oscillations the primary purposethereof is to absorb the entire voltage drop in the circuit during theminute period of time when the condenser 35 is receiving the initialsurge and is functioning as a short circuit for the energy around theX-ray tube.

There is likewise an IR drop across the re- After the expiration of thisperiod of time the current starts to flow sistance element 33 when thecurrent is flowing through the X-ray tube, but as the current is in theorder of hundreds of milliamperes at '75 to kilovolts this drop isimmaterial.

It can thus be readily appreciated by those skilled in the art that Ihave provided an X-ray system for taking short exposure radiographs froma high potential source in which the initial surge of the current isprevented from causing deleterious results to the X-ray tube. Moreover,

the entire period of energization of the X-ray tube is extremely small,but despite the shortness of this period there is an entire absence ofsteepness of the wave form of the energy supplied to the tube, as therise thereof is a gradual one from zero to maximum.

Although I have shown and described one specific embodiment of myinvention I do not desire to be limited thereto as various othermodifications of the same may be made Without departing from the spiritand scope of the appended claims.

What is claimed is:

1. In an X-ray system, the combination with an X-ray tube and a sourceof high potential electrical energy therefor, of means for connectingsaid X-ray tube to said source to cause the sudden energization thereof,and means adapted to be connected in parallel with said X-ray tube andsaid high potential source for retarding the instantaneous supply of theentire energy from said source to said X-ray tube upon the operation ofsaid first mentioned means.

2. In an X-ray system, the combination with an X-ray tube and a sourceof high potential electrical energy therefor, of means for connectingsaid X-ray tube to said source to cause the sudden energizatio-nthereof, and means adapted to be connected in parallel with said X-raytube and said high potential source for retarding the supply of theentire energy of said source to said X-ray tube for a short period oftime upon operation of said first mentioned means to reduce thesteepness of the wave front of the energy supplied to said X-ray tube.

3. In an X-ray system, the combination with an X-ray tube and a sourceof high potential electrical energy therefor, of means for connectingsaid X-ray tube to said source to; cause the sudden energizationthereof, and means associated with said X-ray tube and adapted to beconnected in parallel with the latter and said source, and arranged toreceive a portion of the energy thereof to prevent the entire energy ofsaid source from being initially supplied to said X-ray tube upon theoperation of said first mentioned means.

4. In an X-ray system, the combination with an X-ray tube and a sourceof high potential electrical energy therefor, of means for connectingsaid X-ray tube to said source to cause the sudden energization thereof,and means connected in parallel with said X-ray tube and the source ofenergy therefor and energizable with the said X-ray tube upon operationof said first mentioned means to cause said source to gradually energizeX-ray tube over a minute period of time in order to reduce the steepnessof the wave front of the initial supply of energy to said X-ray tube.

5. In an X-ray system, the combination with an X-ray tube and a sourceof high potential electrical energy therefor, of means for connectingsaid X-ray tube to said source to cause the sudden energization thereof,and means for preventing the immediate supply of energy from said highpotential source through said X-ray tube upon the operation of saidfirst mentioned means comprising a condenser connected in parallel withsaid X-ray tube and said high potential source therefor and adapted tobecome charged by the sudden supply of energy from said source andprohibit the supply thereof to said X-ray tube for a minute period oftime to reduce the steepness of the wave front of the energy when thesame is initially supplied to said X-ray tube.

6. In an X-ray system, an X-ray tube, a source of high potentialelectrical energy for energizing said tube, switching means operable toconnect said X-ray tube to said source, and a condenser connected inparallel with said X-ray tube and said source and energizable with saidtube from said source upon operation of said switching means, saidcondenser adapted to become charged by the initial supply of energy fromsaid source upon operation of said switching means to cause the energysupplied to said X-ray tube to gradually rise from zero to maximum in aminute period of time.

'7. In an X-ray system, a high tension circuit including an X-ray tubeand a source of high potential electrical energy, a second high tensioncircuit including a capacitance and said source, and switching meanscommon to both of said circuits operable to connect said tube and saidcapacitance simultaneously to said source to cause said last mentionedcircuit containing the capacitance to receive the initial supply ofenergy from said source and said first mentioned circuit containing theX-ray tube to become energized vith a gradual rise in the energy fromzero to maximum in a minute period of time after energization of saidsecond mentioned circuit.

8. In an X-ray system, the combination with an X-ray tube and a sourceof high potential electrical energy therefor, of means for suddenlyconnecting said X-ray tube to said source, and means for substantiallyshort-circuiting the supply of energy around said X-ray tube for aperiod of time in the order of micro-seconds after operation of saidfirst mentioned means, said last mentioned means adapted to becomeineffective to short circuit the energy after expiration of said periodof time and effective to cause the energy supplied to said X-ray tube togradually rise from zero to maximum with an absence of a steep wavefront in an equally short period of time after operation of said firstmentioned means.

9. In an X-ray system, an X-ray tube provided with a cathode to beheated, a source of high potential electrical energy for energizing saidtube, a source of low tension energy for supplying heating current tothe cathode of said tube, means for suddenly connecting said X-ray tubeto said high tension source, means for preventing the supply of theentire energy from said source to said X-ray tube for a short period oftime and for causing the supply of energy thereto after the expirationof said period of time, with an absence of steepness in the wave frontof the energy supplied to said X-ray tube, and means connected inparallel with the cathode of said X-ray tube and said low tension sourceto prevent said high tension heavy current source from deleteriouslyafiecting said cathode upon operation of said first mentioned means.

10. In an X-ray system, an X-ray tube provided with a cathode to beheated, a source of high potential electrical energy for energizing saidtube, a source of low-tension energy for supplying heating current tothe cathode of said tube, means for suddenly connecting said X-ray tubeto said high tension source, means to prevent the sudden fiow of energyfrom deleteriously aifecting said tube upon operation of said firstmentioned means, comprising means connected in parallel with theelectrodes of said tube and said source of energy therefor, and adaptedto receive the initial flow of energy for a minute period of time tocause the energy supplied to said X-ray tube to gradually rise in anequally short period of time and obviate possibilities of destroyingsaid tube, and means connected in parallel with the cathode of said tubeand said low tension heating source therefor, and adapted to receive aportion of the initial supply of energy supplied to said X-ray tube toprevent said high potential energy from causing destruction of saidcathode.

11. In an X-ray system, an X-ray tube provided With a cathode to beheated, a source of high potential electrical energy for energizing saidtube, a source of low-tension energy for supplying heating current tothe cathode of said tube, means for suddenly connecting said X-ray tubeto said high tension source, and means to prevent the sudden supply ofenergy from deleteriously affecting said tube upon operation of said,first mentioned means comprising a condenser connected in parallel withthe electrodes of said tube and said high potential source and adaptedto receive the initial supply of energy for a minute period of time tocause the energy supplied to said X-ray tube to gradually rise in anequally short period of time and obviate possibilities of destruction ofsaid tube, and a condenser connected in parallel with the cathode ofsaid X- ray tube and said low tension heating source and adapted toreceive a portion of the initial supply of energy supplied to said X-raytube by said high potential source to prevent the high potential heavycurrent energy from destroying said cathode.

12. In an X-ray system, an X-ray tube provided with a cathode to beheated, a source of high potential electrical energy for energizing saidtube, a source of low-tension energy for supplying heating current tothe cathode of said tube, means for suddenly connecting said X-ray tubeto said high tension source, and means connected in parallel with saidcathode and said low tension source and connected to said high tensionsource to prevent the sudden supply of en ergy therefrom to said X-raytube from deleteriously affecting said cathode upon operation of saidfirstementioned means.

13. In an X-ray system, an X-ray tube provided with a cathode to beheated, a source of high potential electrical energy for energizing isaid tube, a source of low-tension energy for supplying heating currentto the cathode of said tube, means for connecting said X-ray tube tosaid high tension source to cause the sudden energization thereof, andmeans connected in parallel with said cathode and the 10W tensionheating source therefor and connected to said high tension source toprevent the sudden supply of energy therefrom to said X-ray tube fromdeleteriously affecting said cathode upon operation of said firstmentioned means.

14. In an X-ray system, an X-ray tube provided with a cathode to beheated, a source of high potential electrical energy for energizing saidtube, a source of low tension energy for supplying heating current tothe cathode of said tube, a switch for connecting said X-ray tube tosaid high tension source to cause the sudden energization thereof, and acondenser connected in parallel with said cathode and the low tensionheating source therefor and connected to said high tension source toprevent the sudden supply of energy therefrom to said X-ray tube from'deleteriously affecting said cathode upon operation of said firstmentioned means.

MONTFORD MORRISON,

